The determination of the admissible load capacity of a crane so far has been effected for certain set-up or condition parameters to be specified explicitly. There are known for instance indicated load capacities for certain specified ballast stages of the rotary platform of e.g. 10 t (tons) and 20 t or for certain boom lengths and lengths of outreach. The same is true for other parameters, which influence the admissible load capacity of a crane. The admissible values of the load capacity frequently are indicated in the form of load capacity tables, the values of the load capacity usually being indicated in dependence of two parameters. A disadvantage of this procedure is that a determination of the load capacity for arbitrary parameter values freely selectable within a range of parameters is not possible, which results in the disadvantage that the determination of the load capacity is relatively inaccurate.
Therefore, it is the object underlying the present disclosure to develop a method as mentioned above such that the admissible load capacity of a crane can be determined for arbitrary parameter values.
This object is solved by a method in which the load capacity is determined in dependence on at least one first and one second parameter and that the method comprises a first step, in which the load capacity for the value of the first parameter with different values of the second parameter is determined by calculation or by interpolation or extrapolation on the basis of known values of the load capacity for specific values of the first parameter, and that the method comprises a second step, in which the determination of the load capacity for the value of the second parameter is performed on the basis of the load capacity values determined in the first step for different values of the second parameter by calculation or by interpolation or extrapolation.
If it is desired to determine the load capacity for instance in dependence on the parameters of outreach (21.7 m) and main boom angle (83°), the procedure can be as follows: The determination of the admissible load capacity is for instance effected in that for first and second angles (77°; 87°) of the main boom an interpolation of the load capacity is performed by using two points of support from load capacity values known for the different lengths of outreach. It is conceivable, for instance, to perform an interpolation for an outreach of 21.7 m between the points of support at 20 m and 22 m, for which the load capacity is known. This interpolation is performed for a boom angle of 77° as well as for a boom angle of 87°. If it is then desired to determine the load capacity for a boom angle of 83°, a second step then comprises an interpolation between the load capacity values obtained for the boom angle of 77° and for the boom angle of 87°, i.e. in accordance with this example, the second interpolation step employs the points of support obtained in the first step.
Instead of an interpolation or extrapolation, there can also be performed a calculation of the load capacity values, in order to obtain the points of support.
Particularly advantageously, the specific values of the first parameter, for which the load capacity values are known, are chosen in dependence on the values of the second parameter. With reference to the preceding example this means that in contrast to the preceding example, in which identical points of support were used for both main boom angles, the points of support for the interpolation or extrapolation of the load capacity are chosen in dependence on the angle of the main boom. It is advantageous and conceivable when for a larger main boom angle, i.e. with a main boom positioned steeper, smaller values of the outreach are chosen as points of support than for a smaller main boom angle. It is conceivable, for instance, to choose the points of support with a main boom angle of 77° at 20 m and 22 m and with a main boom angle of 87° at 14 m and 16 m. These are, of course, only exemplary values.
The procedure of choosing the specific values of the first parameter, for which the load capacity values are known, in dependence on the values of the second parameter, is of course not only applicable for the parameters of outreach and main boom angle, but also for other parameters, in particular for parameters which exhibit a dependence on each other.
The interpolation or extrapolation can be performed by assuming a linear relationship or also by taking any other functions as a basis, which represent a dependence of the load capacity on the respective parameter.
In principle it is likewise conceivable to perform the determination of the load capacity by calculation. This requires that a connection described by formulae is known between the load capacity and the parameters which have an influence on the load capacity or whose influence should be considered. The calculation of the load capacity thus can be effected by using a formula and parameters from the geometry and basic static data or basic tables.
The method of the present disclosure is not restricted to two independent parameters. Rather, any number of parameters can be considered which have an influence on the load capacity. Thus, it can be provided that the load capacity should be determined in dependence on n parameters, with n≧2, and the method comprising an nth step in which the load capacity is determined by interpolation or extrapolation or by calculation on the basis of the values of the load capacity determined in the (n−1)th step for different values of the nth parameter. This means that the nth step in the determination of the load capacity employs points of support which were determined in the preceding step, i.e. in the (n−1)th step.
The method can be performed with a small number of points of support. In principle it is sufficient when the interpolation or extrapolation is each performed on the basis of two points of support.
Furthermore, it can be provided that the parameters are entered manually. Alternatively or in addition, the determination of the parameters can be effected on the crane by a sensor. In both cases, a continuous adjustment or detection of the parameters preferably is possible. The detection of a parameter by a sensor is expedient in particular when the value has a fixed magnitude (e.g. ballast plate identification) or can be rounded to a fixed magnitude (discretization). The detection of parameters by a sensor is considered for instance in the case of the parameters rotary platform ballast and/or central ballast. Any other parameters, such as the wind speed, can of course also be detected by a sensor.
The parameters included in the calculation of the load capacity preferably are the set-up or condition parameters of the crane.
The parameters which have an influence on the load capacity can be selected from the following non-final group: rotary platform ballast, central ballast (additional undercarriage weight), supporting geometry, wind speed, longitudinal and lateral inclination of the crane, travel speed (in tables on tires or crawler), derrick radius, derrick ballast, angle of rotation of rotary platform, longitudinal and transverse angle of the boom bracing trestle (TA, TY). As regards the supporting geometry, “retracted”, “reduced”, “broad”, 10% steps or finer steps of the sliding beam length can be adjusted instead of firmly specified steps.
When the parameter detected by a sensor varies considerably, as this can for instance be the case with the wind speed, or changes without the action of the crane operator, such as the lateral inclination, the sensor value can be used to preferably permanently switch the load capacity calculation when a parameter limit is exceeded for the first time, such that another, possibly lower parameter value is calculated for the measured sensor value. In this way it is possible to determine a small load capacity which hence is safe in operation.
The present disclosure finally relates to a crane with a unit which includes means for performing one or more of the various methods of the present disclosure. The crane for instance is a derrick crane or a mobile crane, but other types of cranes are also included by the present disclosure.